Electron discharge tube



Dec. 18, 1934. H. ROTHE 1,984,897

ELECTRON DISCHARGE TUBE Filed Jan. 8, 1954 I2 4. /7 f4 5 f5 76 77 .74 25f5 76 IN VEN TOR HORST R0 THE A TTORNEY Patented Dec. 18, 1934 UNITED"STATES PATE . ELECTRON DISCHARGE TUBE Horst Rothe, Berlin, Germany,assignor to Telefunken Gesellschaft graphic in. b. 11., Berlin,

tion of Germany fiir Drahtlose Tele- Germany, a corpora- ApplicationJanuary 8, 1 934,'- -Serial No. 705,649

In Germany June 15, 1932 The present invention relates to an electrondischarge device and more particularly to athermionic tube comprising anindirectly heated cathode, which is to be supplied with alternatingcurrent. 5

The primary object of this invention is to reduce the humming noise,which is caused in a telephone receiver orlOudspeaker by the alternatingheating current.

vAnother object is toenhance the mechanical stability of the electrodesystem. Further objects will become apparent when the specification isperused in connection with the accom panying drawing.

In order to suppress interfering noises in an amplifying tube containingan indirectly heated cathode, it is necessary to keep down the capacitybetween the control electrode and the heater as low as possible. Thisisv of particular importance, when indirectly heated A. C. cathodes areoperated on the full main line voltage. Likewise it may be important fortubes with an extremely large amplification factor, even if operated onlow heating Voltages.

According to the present invention asmall capacity between the controlgrid and the heater is attained by means of a special press, whereby ametal tube is squeezed into a vitreous press, the said tube being thecontinuation of the cathode andelectricaliy connected to it. Whilehitherto some difiiculties have been experienced in hermeticallyembedding metal tubes into a press, these difficulties are, overcome inaccordance with this invention by slipping 'a vitreous tube over themetal tube and, squeezing both together into the press; 'When the pressvis formed, the material of the stem and of the glass tube is softenedand fusedmtogether. The glass tube extends beyond the outward end 40 ofthe metal tube and is sealed ofi there; Fur-- thermore connection wiresto the heater and; the metal tube itself may be led immediately .throughthis seal) As a result of this construction leakage between the metaltube' and the glass in-the press is prevented. a

The joint between the metal tube and the emitting cathode may bescreened by an additional shield, so that no lines of force going outfrom the heater may reach the control electrode 50 and the capacitybetween the heater and the control electrode is reduced to a practicallynegligible value.

An utmost effective screening is attained, when the metal tube projectsto such an extent into the interior of the evacuated vessel that it Theheater is drawn into the interior of the metal tubev in the usualmanner. To prevent heat losses from the incandescent .cathode' bythermal conduction away towardsithe press,

slots maybe provided nearthe end of the incandescent part of thecathode.I

When the vitreoustube slipped over the metal tubeis not sealed off atthe outward end and the connection wires are led through the side wallof the tube, it may be used for connecting the discharge device to theexhausting pump. If the square section of the metal tubeis filled upbythe heater, another exhaustion tube is to be'sealed into the press. vIf the metal tube squeezed into the press is stronglyconnected to thecathode, it renders the whole electrode'system very resistant tomechanical shocks and vibrations so that tubes manufactured inaccordance with this principle exhibita relatively small microphoniceifect.

Fig. 1 shows one form of my invention. Fig.2 shows a modified form of myinvention. One method of carrying this invention into effect will now bedescribed with reference to Fig. 1,0f the drawing. A reentrant stem isindicated by 1. The vessel-enclosing the electrode system and fused tothe stern is omitted. 2 is the press, Where the leading-in wires and thesupports carrying the electrodes aresealed in.

3 denotesa. metal tube, preferably; consisting of a refractory metal,while 4 is vitreous tube slipped over the metal tube 3. Both, aresqueezed together into the press. The lower end of the vitreous tube 4is sealed oifat 4. The metalsleeve carrying the emitting; layer ofthecathode is indicated by 5 ;.it is connected to the metal tubeB- at 7.-As shown, the metal tube 3 laps over the,;;;lower--edge of the cathodesleeve the: discharge space. Inside the cathode sleeve the heater8 islocated. Current is supplied to the heater through the wires 9, 10;which are sealed into the glass tube at 4.. Another leadtube 3 andthereby alsoto the cathode sleeve 5.

The'catho'de 5-is surrounded'by a' grid electrode consisting of a wire12 helically wound on two supporting rods 13, 14, which are sealed at,5-thereby perfectly shielding the heater against ing-in conductor 11 isconnected to the metal T OFFlC E proper spaced relation and render theelectrode system stable.

In Fig. 2 a modified form of the invention is illustrated, which is inmany respects similar to the construction of the tube in Fig. 1. In bothfigures. like reference numerals are used to designate. like parts. Thecathode sleeve and the shielding metal tube are combined as a singlemetal tube 25. In this way the mechanical stability of the electrodesystem is considerably enhanced and more effective shielding between thecontrol electrode and the heater is accomplished. In order to preventtoo rapid thermal conduction away from the emitting part of the cathode,slots 26 are provided in the metal tube between the press 2 and theincandescent part of the cathode. A separate exhaust tube is indicatedby 2'7, which is drawn off at 28.

It will be understood that the embodiments of the invention disclosedare merely illustrative and that many modifications and alterations maybe made therein without. departing from the-spirit and the scope of thisinvention.

Having described my invention I claim as new and desire to secure byLetters Patent:

1. An electron discharge tube provided with a reentrant stem terminatingin a press, an indirectly heated cathode having a metal tube located inthe prolongation of the cathode and electrically connected thereto, themetal tube passing through the press and projecting therefrom, currentsupply wires to the cathode heater led: inside the metal tube, avitreous tube slipped over the projecting part of the metal tube andsqueezed into the press at one end and sealed off at the'other end.

22An electron discharge tube comprising an evacuated envelope providedwith a hollow reentrant stem--terminating in an inwardlyprojecting'press; a plurality of electrodes extending aboveand supportedfrom said press, an insulating tube fused' to and extending outwardlyfrom the press and communicating with the space within the envelope, anindirectly heated cathode mounted above the press and having aprolbngation extending within the insulating tube, and a-pain of-heaterleads extending from the cathode through its prolongation and sealed tothe outerend-of the insulating tube.

- 33' An electron discharge tube comprising an evacuated envelopeprovided with a hollow reentrant stem terminating in an inwardlyprojecting press, a plurality of electrodes extending above andsupported from said press, an insulating tube fused to and extendingoutwardly from the press and communicating with the space within theenvelope, an indirectly heated cathode and a heater therefor mountedabove the-press, a pair of heaterleads extending from the cathodethrough the insulating tube and sealed tothe outer endof the insulatingtube, andametallic shielding sleeve surrounding the heater leads anddisposed within the insulating tube;

4. An electron discharge tube comprising an evacuated. envelope providedwith a hollow reentrantstem terminating in an inwardly projecting press,a plurality of electrodes extending above and supported from said press,an insulating tube fused to and extending outwardly from the press forsubstantially the full length of the stern and communicating with thespace withinthe envelope, an indirectly heated cathode and. a' heatertherefor mounted above the press, a shielding tube disposed within theinsulating tube and extending above the press, and a pair of heaterleads extending from the oathode through the shielding tube and sealedto the outer end of the insulating tube.

5. An electron discharge tube comprising an evacuated envelope providedwith a hollow reentrant stem terminating in an inwardly projectingpress, a plurality of electrodes extending above and supported from saidpress, an insulating tube fused to and extending outwardly from thepress for substantially the full length of the stem and communicatingwith the space within the envelope, an indirectly heated cathode and aheater therefor mounted above the press, a shielding tube disposedwithin the insulating tube and extendingabove the press, and a pair ofheater leads extending from thecathode through the shielding tube andsealed to the outer end of the insulating tube, a lead wire for saidshielding tube also sealed to the outer end of the insulating tube, andan electrical connection between the shilding tubeand. the

cathode. l

6. An electron discharge tube comprising. an evacuated envelope providedwith ahollow reentrant stem terminating in an inwardly projecting press,a plurality of electrodes extending above and supported from said press,an insulating tube fused to and extending. outwardly from the press forsubstantially the full length of the stern and communicating with thespace within the envelope, an indirectly heated cathode and a heatertherefor mounted above the press and having a prolongation integraltherewith extending within the insulating tube, and a pair of heaterleads extendingfrom the cathode through its prolongation and sealed tothe outer end of the insulating tube.

'7. An electron. discharge tube comprising an evacuated envelopeprovided witha hollow reentrant stem terminating in an inwardlyprojecting press, a plurality of electrodes extending u above andsupported from said press, an insulating. tube fused to and extendingoutwardly from the press for substantially the full length of the sternand communicating with the space within the envelope, an elongatedtubular sleeve having its lower portion housed within theinsulatingtube, the upper: portion of said tubular sleeve constituting acathodeand being coated with electron emitting material and extending upwardlyin cooperative relationwith the aforesaid electrodes, said portionshaving between them a series of longitudinal slats-for preventing toorapid heat radiation. fromthe c'athode,.and a pair of heater leads and acathode lead sealed to the outer end of the insulating tube.

HORST ROTHE.

